Even as the world's first malaria vaccine gets closer to the market, two leading drug firms have joined forces to test a next-generation shot against the mosquito-borne disease that kills 800,000 people a year. GlaxoSmithKline (GSK.L) and Johnson & Johnson (JNJ.N), through its newly acquired Dutch unit Crucell, plan to start a clinical trial using the so-called "prime-boost" vaccine within the next couple of months.